1. Technical Field of the Invention
The present invention relates generally to an automotive air conditioning system designed to automatically switch between an air recirculation mode and a ventilation mode according to a measure of contamination of ambient air, and more particularly to such an automotive air conditioning system designed to control the switching between the air recirculation mode and the ventilation mode according to the vehicle speed.
2. Background of Related Art
Automotive air conditioning systems are known in the art which has an air contamination sensor disposed outside of a passenger compartment of a vehicle and which switches a ventilation mode to an air recirculation mode automatically when it is determined based on a sensor output that surrounding air is polluted (which will be referred hereinafter as automatic recirculation/ventilation mode control).
Usually, in winder, when an automotive vehicle is traveling at high speeds, window glasses are blown by the lower-temperature wind and cooled, so that they are fogged up easier than when the vehicle is parked.
As compared with when the vehicle is parked, the flow rate of air discharged from an air conditioner in the ventilation mode is increased by the traveling-induced wind, but it is kept in the air recirculation mode whether the vehicle is traveling or parked.
In analysis of air conditioning comfort in the above conventional air conditioning systems during traveling of the vehicle, the inventors of this application have encountered the following problems.
When the vehicle travels at a high speed during air conditioning operation in the automatic recirculation/ventilation mode control, the air recirculation mode is entered so that window glasses become apt to be fogged, which may obstruct the view of the driver.
When switching between the air recirculation mode and the ventilation mode is performed during traveling of the vehicle at a high speed (e.g., 150 km/h), it will result in a great difference in flow rate of air discharged to a passenger compartment with which vehicle occupants feel uncomfortable.